Brazil’s biggest newspaper has printed an illustration from a Marvel comic of two men kissing on its front page to attack an attempt at censorship by the evangelical mayor of Rio de Janeiro.

Marcelo Crivella attempted to ban copies of the graphic novel Avengers: The Children’s Crusade from appearing at a book fair on the grounds that it included content unsuitable for children.

Critics said his move was reminiscent of the censorship imposed during Brazil’s 21-year military dictatorship, which ended in 1985 and is often praised by the country’s far-right president, Jair Bolsonaro. On Sunday the president of Brazil’s supreme court overruled a court decision that had endorsed Crivella’s move.

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Folha de S.Paulo’s mission was to “throw light on censorship threats”, its editor, Sérgio Dávila, told the Guardian.

“It is an attack on freedom of expression,” said Mariana Zahar, the vice-president of the National Union of Book Publishers, which organised the book fair. “We will fight this to the end.”

The controversy began on Thursday when Crivella ordered the biennial to wrap copies of the graphic novel in black plastic. “What we did was defend the family,” Crivella said in a video he tweeted on Friday after ordering city hall inspectors to seize copies of the book – which had apparently sold out by that point anyway.

“It is a backwards decision … it is ignorant censorship,” said Marcelo Chalréo, the president of the commission of social rights at Rio’s bar association, which has also attacked the legality of Crivella’s move.

Felipe Neto, a YouTube celebrity with 34 million followers, bought 14,000 copies of books with LGBT themes at the book fair and gave them out for free, wrapped in black plastic with the warning: “Book inappropriate for backward … and prejudiced people.” Demonstrators marched through the event, wrapped in rainbow colours and waving placards and books, while gay couples kissed in protest.

Neto linked Crivella’s move to the government of Bolsonaro, who has repeatedly made homophobic comments. Bolsonaro watched an independence day military parade on Saturday with Crivella’s uncle, the evangelical bishop Edir Macedo, the founder of the powerful Universal Church of the Kingdom of God.

“Although we [are] going through the most frightening government in terms of repression since the dictatorship, this time we have a united and engaged people who will not permit that censorship, the imposition of others’ moral values,” Neto told the Guardian.